Pneumatic servomotor comprising a diaphragm and/or a joint which is overmoulded onto the skirt

ABSTRACT

A pneumatic servomotor ( 12 ) for an assisted braking having a rigid axial casing ( 16 ) with a movable substantially truncated-cone shaped transverse skirt ( 18 ) that is integral with a piston ( 20 ) for the actuation of an associated master cylinder ( 14 ) that defines two pressure chambers ( 24, 26 ) inside the casing. A substantially annular sealing diaphragm ( 30 ) made of an elastomeric material is interposed between the casing ( 16 ) and an outer peripheral area ( 32 ) of the skirt ( 18 ) has a substantially annular seal ( 34 ) made of an elastomeric material is interposed between an inner area of the skirt ( 18 ) and the piston ( 20 ). The sealing diaphragm ( 30 ) and the seal ( 34 ) have a portion that is moulded over the skirt ( 18 ).

BACKGROUND OF THE INVENTION

This invention relates to a pneumatic servomotor for an assistedbraking.

More particularly, the present invention relates to a pneumaticservomotor for an assisted braking, of the type comprising a rigid axialcasing, in which a substantially truncated-cone shaped transverse skirtis movable and integral with a piston for the actuation of an associatedmaster cylinder, while it defines two pressure chambers inside thecasing; of the type in which a substantially annular sealing diaphragmmade of an elastomeric material is interposed between the casing and anouter peripheral area of the skirt; and of the type in which asubstantially annular seal made of an elastomeric material is interposedbetween an inner area of the skirt and the piston.

Numerous implementations of servomotors of said type are well known.

According to a first known design, servomotors were provided, in whichbearing faces of the sealing diaphragm and/or of the seal wereaccommodated inside a groove in the piston. Yet such design has thedisadvantage of requiring a careful fitting of the bearing faces inquestion into the associated grooves, failing which some lack oftightness may occur between the skirt and the seal or between the skirtand the diaphragm, thus connecting the front chamber with the rearchamber of the servomotor.

In order to cope with such a drawback, a second design has beensuggested, according to which a diaphragm is made in one piece with theseal and conforms to the rear face of the skirt.

The latter design theoretically eliminates any possible lacks oftightness, likely to appear between the skirt and the seal or betweenthe skirt and the diaphragm, yet no particular arrangements are made forthe elastomeric material to adhere to the skirt in a reliable manner.Should such material happen to separate from the skirt, then it mightbecome slack and impair the tightness between the seal and the skirt, orthe tightness between the diaphragm and the skirt.

SUMMARY OF THE INVENTION

In order to cope with such a drawback, the present invention provides aservomotor comprising a sealing diaphragm and/or a seal, attached toboth sides of the skirt.

To this end, the invention provides a servomotor of the above-describedtype, characterised in that the sealing diaphragm and/or the sealcomprise(s) a portion, which is moulded over the skirt.

According to other characteristics of the present invention:

-   -   an annular portion of the diaphragm, which faces the axis of the        servomotor, covers both sides of an outer peripheral        truncated-cone shaped area of the skirt, and fills at least a        first through-thickness channel provided in said outer        peripheral area of the skirt, so as to ensure a continuity of        the elastomeric material of the diaphragm;    -   the channel is situated facing a projection, formed in the outer        peripheral truncated-cone shaped area of the skirt, and intended        to constitute an accumulation area for the elastomeric material        of the diaphragm, for a more reliable strength of said        elastomeric material close to the channel;    -   the inner area of the skirt is tubular and it comprises a front        tubular section, encompassing a cylindrical bearing face of the        piston, and a rear tubular section having a smaller diameter        than that of the cylindrical bearing face, and capable of being        deformed and/or of being fitted into a groove provided in the        piston, rearwards of the cylindrical bearing face;    -   the seal lies on both sides of the front tubular section and        fills at least a through-thickness hole in said front tubular        section, so as to ensure a continuity of the elastomeric        material of the seal;    -   the seal comprises at least one annular lip, which is interposed        between the inner side of the front tubular section and the        piston;    -   the seal extends over the full length of the front tubular        section, and the hole provided in the front section is a radial        one;    -   the front section comprises a shoulder-forming wall, connecting        it to the rear section, and the hole provided in the front        section traverses said shoulder-forming wall axially, whereas        the seal extends on both sides of the shoulder-forming wall, and        the annular lip is disposed in line with the hole;    -   the skirt is manufactured using a stamping process, carried out        on a sheet-metal blank, and the channel consists of a bored        hole;    -   the edge of the outer peripheral truncated-cone shaped area of        the skirt, which is situated radially outwards of the        projection, comprises a folding over of the blank sheet, so as        to strengthen the skirt at its outer periphery;    -   the fold extends at least in part opposite the projection in        order to confine the elastomeric material of the diaphragm in        the projection;    -   the skirt is moulded from a plastic material, and the channel        consists of a baffle extending through the outer peripheral        truncated-cone shaped area of the skirt;    -   the rear face of the edge of the outer peripheral truncated-cone        shaped area, which is situated radially outwards of the        projection, comprises at least two concentric annular teeth so        as to fix the elastomeric material of the diaphragm in position        on the skirt;    -   the diaphragm is made in one piece with the seal.    -   Other features and advantages of the present invention will be        apparent from the following detailed description, when taken in        conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is an axial sectional view of a servomotor according to a priorart;

FIG. 2 is a detail axial sectional view of the outer peripheral area ofthe skirt of the servomotor according to Detail II indicated in FIG. 1;

FIG. 3 is a detail axial sectional view of the inner area of the skirtof the servomotor according to Detail III indicated in FIG. 1;

FIG. 4 is a detail axial sectional view of a first embodiment of theouter peripheral area of the sheet-metal skirt of a servomotor accordingto the present invention;

FIG. 5 is a detail axial sectional view of a second embodiment of theouter peripheral area of the sheet-metal skirt of a servomotor accordingto the present invention;

FIG. 6 is a detail axial sectional view of a first embodiment of theouter peripheral area of the plastic skirt of a servomotor according tothe present invention;

FIG. 7 is a detail axial sectional view of a second embodiment of theouter peripheral area of the plastic skirt of a servomotor according tothe present invention;

FIG. 8 is a detail axial sectional view of a first embodiment of theinner area of the sheet-metal skirt of a servomotor according to thepresent invention; and

FIG. 9 is a detail axial sectional view of a second embodiment of theinner area of the sheet-metal skirt of a servomotor according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, the same reference numerals will designatethe same elements, or elements having similar functions.

As a rule, the terms “front”, “rear”, “upper” and “lower” referrespectively to elements or positions facing leftwards, rightwards,upwards or downwards in the figures.

FIG. 1 shows a servobrake 10 for a motor vehicle, comprising abraking-assistance pneumatic servomotor 12, which actuates a brakingmaster cylinder 14.

In a well-known manner, the servomotor 12 comprises a rigid axial casing16, in which a substantially truncated-cone shaped skirt 18 is movablymounted in an airtight manner, such skirt being integral with a piston20 for the actuation of the associated master cylinder 14, through apush rod 22.

As is well known too, the skirt 18 defines, inside the casing 16, twopressure chambers, namely a front pressure chamber 24 and a rearpressure chamber 26, which may be subjected to different pressures, soas to achieve the travel of the skirt 18 and, accordingly, the actuationof the push rod 22.

Since such a configuration is known from the state of the art, it willnot be further described herein.

In a well-known manner, a sealing diaphragm 30, which is substantiallyannular and made of an elastomeric material, is interposed between thecasing 16 and an outer peripheral area 32 of the skirt 18, and a seal34, which is substantially annular and made of an elastomeric material,is interposed between an inner area 36 of the skirt 18 and the piston20. According to the state of the art, the diaphragm 30 and the seal 34may be made in one piece, as shown in FIG. 1 in which the diaphragm 30and the seal 34 are continuous and cover the whole rear face 31 of theskirt 18, but such an arrangement is in no way limitative of the knownconfigurations, and designs according to which the diaphragms 30 and theseals 34 are independent of each other are also well known from thestate of the art.

FIG. 2 represents the diaphragm 30 as indicated by Detail II in FIG. 1,whereas FIG. 3 shows the seal 34 as indicated by Detail III in FIG. 1.

As appears from FIG. 2, generally the diaphragm 30 is merely attached tothe rear face 31 of the skirt 18, for instance by adhesive bonding, orby a vulcanization in the course of the manufacturing of the diaphragm30. But, owing to the fact that the diaphragm 30 does not extend ontothe front face 33, the air inside the rear chamber 26 may escape to thefront chamber 24, should the diaphragm 30 happen to separate from theskirt 18.

Similarly, as illustrated in FIG. 3, generally the seal 34 is fixed inposition between the rear face 31 of the skirt 18 and a front end wall38 of a groove 40 provided in the piston 20, more particularly becausethe seal 34 is fitted into the groove. But, owing to the fact that theseal 34 does not extend onto the front face 33, if the seal 34 happensto separate from the skirt 18, the air inside the rear chamber 26 maypass round the seal 34, escape through the groove 40 and the end 42 ofthe skirt 18 and flow into the front chamber.

So as to cope with the above-mentioned drawbacks, FIG. 4 et seq show aservomotor 12 according to this invention and of the above-describedtype, characterised in that the sealing diaphragm 30 and/or the seal 34comprises a portion which is moulded over the skirt 18.

For this purpose, as shown in FIGS. 4 through 7, an annular portion 44of the diaphragm, which faces the axis of the servomotor 12, covers bothsides corresponding to the faces 31 and 33 of the outer peripheraltruncated-cone shaped area 32 of the skirt 18, and fills at least afirst through-thickness channel 46 provided in said outer peripheralarea 32 of the skirt 18, so as to ensure a continuity of the elastomericmaterial of the diaphragm 30. Therefore, the filling of the channel 46is carried out in the course of the polymerization of the elastomericmaterial of the diaphragm 30.

More specifically, the channel 46 is situated facing a projection 48,formed in the outer peripheral truncated-cone shaped area 32 of theskirt 18. Such projection 48 is intended to constitute an accumulationarea 49 for the elastomeric material of the diaphragm 30, for a morereliable strength of said elastomeric material close to the channel 46.In particular, thanks to such an arrangement, a shear of the material ofthe diaphragm 30 across the channel 46 may be avoided.

FIGS. 4 and 5 show that the skirt 18 may be manufactured using astamping process, carried out on a sheet-metal blank, in which case thechannel 46 consists of a bored hole, and the projection 48 is formed inthe course of the stamping of the blank out of which the skirt 18 isshaped.

According to a first embodiment of the sheet-metal skirt 18 as shown inFIG. 4, the skirt 18 is stamped so as to have the same thicknessthroughout.

According to a second embodiment of the sheet-metal skirt 18 as shown inFIG. 5, the skirt 18 may be stamped and then doubled upon itself so asto exhibit a twofold thickness locally.

Thus, the edge 50 of the outer peripheral truncated-cone shaped area 32,which is situated radially outwards of the projection 48, comprises afold 52 of the sheet metal of the blank, so as to strengthen the skirt18 at its outer periphery.

In an advantageous manner, an end 54 of the fold 52 extends at least inpart opposite the projection 48 in order to confine the elastomericmaterial of the diaphragm 30 in the projection 48.

FIGS. 6 and 7 show that the skirt 18 may be moulded from a plasticmaterial, in which case the channel 46 consists of a baffle extendingthrough the outer peripheral truncated-cone shaped area 32 of the skirt18. The skirt 18 comprises a projection 48 which, similarly to theabove-described one, is intended to constitute an accumulation area 49for the elastomeric material of the diaphragm 30, for a more reliablestrength of the elastomeric material close to the channel 46. Mostadvantageously, the projection 48 is formed during the moulding of theplastic material for the skirt 18.

Quite advantageously too, a lug 53, similar to the end 54 of the fold52, as hereinabove described with reference to FIG. 5, extends at leastin part opposite the projection 48, in order to confine the elastomericmaterial of the diaphragm 30 in the projection 48.

According to a first embodiment of the skirt made of a plastic materialas shown in FIG. 6, the edge 50 of the outer peripheral truncated-coneshaped area 32 is smooth.

According to a second embodiment of the skirt made of a plastic materialas shown in FIG. 7, the rear face 31 of the edge 50 of the outerperipheral truncated-cone shaped area 32, which is situated radiallyoutwards of the projection 48, comprises at least two concentric annularteeth 56, so as to fix the elastomeric material of the diaphragm 30radially in position on the skirt 18. Said teeth contribute to theinterpenetration of the elastomeric material of the diaphragm 30 and ofthe plastic material of the skirt 18.

In a similar manner, FIGS. 8 and 9 illustrate a first and a secondembodiments of the seal 34 associated with a skirt 18. In these figures,the skirt 18 is shown as a skirt 18 formed out of a stamped sheet-metalblank but it goes without saying that the skirt 18 might just as wellconsist of a moulded plastic material, as set forth hereinabove.

FIGS. 8 and 9 show that the inner area 36 of the skirt 18 comprises afront tubular section 58, encompassing a cylindrical bearing face 60 ofthe piston 20, and a rear tubular section 62 having a smaller diameterthan that of the cylindrical bearing face 60, and capable of beingdeformed and/or of being fitted into a groove 64 provided in the piston,rearwards of the cylindrical bearing face 60. More particularly, whenthe skirt 18 is made out of sheet metal, the section 62 is designed fora deformation, in the direction of the arrows in FIGS. 8 and 9, so as toreach the bottom of the groove 64 whereas, if the skirt 18 consists of aplastic material, the section 62 conforms to the shape of the groove 64,and it will become deformed so as to fit into said groove 64.

Whatever the contemplated embodiment may be, the seal 34 lies on bothsides 31, 33 of the front tubular section 58, and it fills at least athrough-thickness hole 66 in said front tubular section 58, so as toensure a continuity of the elastomeric material of the seal 34.

Besides, the seal 34 comprises at least one annular lip 68, which isinterposed between the inner side, corresponding to the face 33 of thefront tubular section 58, and the piston 20.

According to the first embodiment, as illustrated in FIG. 8, the seal 34extends over the full length of the front tubular section 58, and thehole 66 in the front section 58 is a radial one.

According to this arrangement and in a preferred manner, the seal 34comprises a plurality of lips 68, in contact with the bearing face 60 ofthe piston 20.

In a second embodiment, as represented in FIG. 9, the front section 58comprises a shoulder-forming wall 70, connecting it to the rear section62. The hole 66 provided in the front section 58 traverses saidshoulder-forming wall 70 axially, whereas the seal 34 extends on bothsides 31, 33 of the shoulder-forming wall 70, and the annular lip 68 isdisposed in line with the hole 66 and in contact with a front end wall72 of the groove 64 provided in the piston 20.

In the preferred embodiment of this invention, the diaphragm 30 is madein one piece with the seal 34, and it covers the front face 31 and therear face 33 of the skirt 18. Of course, such an arrangement is by nomeans limitative of the invention, and the diaphragm 30 and the seal 34may be independent of each other.

Quite advantageously therefore, this invention makes it possible toimprove the tightness and to reduce a leakage risk between the skirt 18and the diaphragm 30 and/or the seal 34 of a servomotor 12.

1. A pneumatic servomotor (12) for assisted braking comprising a rigidaxial casing (16), in which a substantially truncated-cone shapedtransverse skirt (18) is movable and integral with a piston (20) for theactuation of an associated master cylinder (14), said skirt defining twopressure chambers (24, 26) inside the casing in which a substantiallyannular sealing diaphragm (30) made of an elastomeric material isinterposed between the casing (16) and an outer peripheral area (32) ofthe skirt (18); and in which a substantially annular seal (34) made ofan elastomeric material is interposed between an inner area (36) of theskirt (18) and the piston (20), characterized in that the sealingdiaphragm (30) and/or the seal (34) comprise(s) a portion, which ismoulded over the skirt (18), said portion including an annular portion(44) of the diaphragm (30), that faces the axis of the servomotor (12),covers both sides (31, 33) of an outer peripheral truncated-cone shapedarea (32) of the skirt (18), and fills at least a first throughthickness channel (46) provided in said outer peripheral area (32) ofthe skirt (18), so as to ensure a continuity of the elastomeric materialof the diaphragm (30), said channel (46) is situated facing a projection(48), formed in the outer peripheral truncated-cone shaped area (32) ofthe skirt (18), creating an accumulation area (49) for the elastomericmaterial of the diaphragm (30) to provide more reliable strength of saidelastomeric material close to the channel (46).
 2. The pneumaticservomotor (12) according to claim 1 characterised in that the innerarea (36) of the skirt (18) is tubular. And in that it comprises a fronttubular section (58) encompassing a cylindrical bearing face (60) of thepiston (20), and a rear tubular section (62) having a smaller diameterthan that of the cylindrical bearing face (60), and capable of beingdeformed and/or of being fitted into a groove (64) provided in thepiston (20), rearwards of the cylindrical bearing face (60).
 3. Thepneumatic servomotor (12) according to claim 2, characterised in thatthe seal (34) lies on both sides (31, 33) of the front tubular section(58), and fills at least a through-thickness hole (66) provided in saidfront tubular section (58), so as to ensure a continuity of theelastomeric material of the seal (34).
 4. The pneumatic servomotor (12)according to claim 3, characterised in that the seal (34) comprises atleast one annular lip (68), which is interposed between the inner side(33) of the front tubular section (58) and the piston (20).
 5. Thepneumatic servomotor (12) according to claim 4, characterized in thatthe seal (34) extends over the full length of the front tubular section(58), and in that the hole (66), provided in the front section, is aradial one.
 6. The pneumatic servomotor (12) according to claim 4,characterised in that the front section (58) comprises ashoulder-forming wall (70), connecting it to the rear section (62), inthat the hole (66) provided in the front section traverses saidshoulder-forming wall (70) axially, and in that the seal (34) extends onboth sides (31, 33) of the shoulder-forming wall (70), whereas theannular lip (68) is disposed in line with the hole (66).
 7. Thepneumatic servomotor (12) according to claim 6, characterised in thatthe skirt (18) is manufactured using a stamping process, carried out ona sheet-metal blank, and in that the channel (46) consists of a boredhole.
 8. The pneumatic servomotor (12) according to claim 7,characterised in that the edge (50) of the outer peripheraltruncated-cone shaped area (32), which is situated radially outwards ofthe projection (48), comprises a fold (52) of the blank sheet, so as tostrengthen the skirt (18) at its outer periphery.
 9. The pneumaticservomotor (12) according to claim 6, characterised in that the fold(52) extends at least in part opposite the projection (48), in order toconfine the elastomeric material of the diaphragm (30) in the projection(48).
 10. The pneumatic servomotor (12) according to claim 6,characterised in that the skirt (18) os moulded from a plastic material,and in that the channel (46) consists of a baffle extending through theouter peripheral truncated-cone shaped area (32) of the skirt (18). 11.The pneumatic servomotor (12) according to claim 10, characterised inthat the rear face (31) of the edge (50) of the outer peripheraltruncated-cone shaped area (32), which is situated radially outwards ofthe projection (48), comprises at least two concentric annular teeth(56), so as to fix the elastomeric material of the diaphragm (30)radially in position on the skirt (18).
 12. The pneumatic servomotor(12) according to claim 11, characterised in that the diaphragm (30) ismade in one piece with the seal (34).